Question

Two convex lens L1 and L2 having focal length 20 cm and 40 cm respectively are placed coaxially in closed contact, this system of lenses is again placed coaxially in closed contact with a concave lens L3 of focal length 1 metre. The effective focal length of the combination will be:
a)13 cm b)200/13 cm c)40/3 cm d)-40 cm

Answer 1

Answer:

yes you are right so c

and in this way I have given wrong answer